Iranian authorities have banned a newspaper allied to presidential candidate Mehdi Karroubi after he denounced Iran's government as "illegitimate" because of claims of voting fraud in last month's election, a reformist political group said Wednesday.

The closure of the daily Etemad-e-Melli, or National Confidence, is another blow by officials seeking to block media and Web sites critical of President Mahmoud Ahmadinejad, whose disputed June 12 re-election was confirmed this week by Iran's powerful Guardian Council.

Karroubi, a former parliament, received only a fraction of the votes in the results announced by authorities and joined opposition leader Mir Hossein Mousavi in demanding a new election. Recently, however, Karroubi has stepped up his independent criticism of the election and could emerge as a leading dissident voice against Ahmadinejad.

On Tuesday, he issued a harshly worded statement that blasted Ahmadinejad's government and pledged to continue challenging its authority. Karroubi's political group, the National Confidence Party, said the newspaper was shut down in response.

"I don't consider this government as legitimate," said the statement posted on Karroubi's Wed site. "I will continue the fight under any circumstances and using every means."

Ahmadinejad canceled plans to travel to Libya as an observer at an African Union summit, Libyan officials said. It would have been Ahmadinejad's second trip outside Iran since the election.

No reason was given for the last-minute cancellation, but some African officials had complained that Ahmadinejad's presence at the three-day gathering could divert attention from Africa's problems.

Ahmadinejad on Tuesday repeated the claims that post-election street riots were linked to a "soft revolution" aided by foreign powers.

"Enemies, despite overt and covert conspiracies to topple (the ruling system) through a soft overthrow, failed to reach their goals," state television quoted Ahmadinejad as telling Intelligence Ministry officials.

It's unclear how many people have been detained during the post-election riots and protests, but at least one group, the Paris-based International Federation of Human Rights, claimed at least 2,000 arrests have been made. Officials place the death toll at 17 protesters and eight security forces, but the figures could be not independently verified because of media restrictions.

Iran's cleric-led government has said Ahmadinejad would be sworn in for a second four-year term as early as July 26.

EDITOR'S NOTE: Iranian authorities have barred journalists for international news organizations from reporting on the streets and ordered them to stay in their offices. This report is based on the accounts of witnesses reached in Iran and official statements carried on Iranian media.